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initial sbfd api
Signed-off-by: Jason Bos <jbos@cisco.com>
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‎doc/BFD/Seamless-BFD.md‎

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# Seamless BFD (S-BFD)
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Title | Seamless BFD (S-BFD)
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------------|----------------
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Authors | Jason Bos
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Status | In review
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Type | Standards track
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Created | 10/10/2025
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SAI-Version | 1.16
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Seamless Bidirectional Forwarding Detection (S-BFD) provides a simplified mechanism for continuity testing and validation of forwarding paths. Unlike traditional BFD, S-BFD does not require session establishment or negotiation - instead, it uses a reflector model where one side (the initiator) can immediately begin sending BFD packets to the other side (the reflector) without coordinated session state.
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S-BFD is useful for:
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- Rapid path validation without session overhead
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- Monitoring with minimal state on reflectors
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- Validation of return paths in asymmetric routing scenarios
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- Scaling to large numbers of monitored paths
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SAI supports S-BFD through two session types:
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```
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typedef enum _sai_bfd_session_type_t
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{
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...
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/** S-BFD Reflector */
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SAI_BFD_SESSION_TYPE_REFLECTOR,
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/** S-BFD Initiator */
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SAI_BFD_SESSION_TYPE_INITIATOR,
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...
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} sai_bfd_session_type_t;
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```
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### S-BFD Reflector
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The S-BFD reflector operates in a stateless manner. When configured, the reflector:
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- Listens for incoming S-BFD control packets
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- Reflects packets back to the initiator
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- Does not maintain per-session state
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- Uses the local discriminator to identify the reflector endpoint
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Key attributes for a reflector session:
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- `SAI_BFD_SESSION_ATTR_TYPE`: Set to `SAI_BFD_SESSION_TYPE_REFLECTOR`
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- `SAI_BFD_SESSION_ATTR_LOCAL_DISCRIMINATOR`: Identifies the reflector (must be well-known)
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- `SAI_BFD_SESSION_ATTR_SRC_IP_ADDRESS`: Source IP for reflected packets
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### S-BFD Initiator
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The S-BFD initiator actively monitors paths by sending S-BFD control packets. The initiator:
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- Sends S-BFD packets with the reflector's discriminator as the destination
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- Monitors returned packets to verify path continuity
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- Maintains session state and detects failures based on timeout
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- Can dynamically adjust monitoring parameters
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## Usage Example: S-BFD Reflector
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The following example demonstrates how to configure an S-BFD reflector on a network device. The reflector uses a well-known discriminator (4) that initiators will use to send S-BFD packets.
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```c
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/*****************************************************
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* Create an S-BFD Reflector Session
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*
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* This reflector will:
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* - Listen on discriminator 4
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* - Reflect S-BFD packets back to any initiator
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* - Operate statelessly
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*****************************************************/
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sai_object_id_t sbfd_reflector_session;
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std::vector<sai_attribute_t> attrs;
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sai_attribute_t attr;
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// Set session type to reflector
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attr.id = SAI_BFD_SESSION_ATTR_TYPE;
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attr.value.s32 = SAI_BFD_SESSION_TYPE_REFLECTOR;
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attrs.push_back(attr);
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// Set local discriminator (well-known value for this reflector)
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attr.id = SAI_BFD_SESSION_ATTR_LOCAL_DISCRIMINATOR;
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attr.value.u32 = 4;
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attrs.push_back(attr);
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// Set hardware lookup valid to true for packet processing
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attr.id = SAI_BFD_SESSION_ATTR_HW_LOOKUP_VALID;
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attr.value.booldata = true;
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attrs.push_back(attr);
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// Set virtual router for routing lookup
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attr.id = SAI_BFD_SESSION_ATTR_VIRTUAL_ROUTER;
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attr.value.oid = vrf_id; // Virtual router object
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attrs.push_back(attr);
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// Set source IP address (reflector's IP)
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attr.id = SAI_BFD_SESSION_ATTR_SRC_IP_ADDRESS;
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attr.value.ipaddr.addr_family = SAI_IP_ADDR_FAMILY_IPV4;
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inet_pton(AF_INET, "192.0.2.1", &attr.value.ipaddr.addr.ip4);
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attrs.push_back(attr);
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// Set IP header version
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attr.id = SAI_BFD_SESSION_ATTR_IPHDR_VERSION;
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attr.value.u8 = 4;
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attrs.push_back(attr);
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// Set encapsulation type (no encapsulation for basic S-BFD)
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attr.id = SAI_BFD_SESSION_ATTR_BFD_ENCAPSULATION_TYPE;
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attr.value.s32 = SAI_BFD_ENCAPSULATION_TYPE_NONE;
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attrs.push_back(attr);
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// Optional: Set TTL for reflected packets
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attr.id = SAI_BFD_SESSION_ATTR_TTL;
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attr.value.u8 = 255;
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attrs.push_back(attr);
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// Optional: Set TOS/DSCP for reflected packets
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attr.id = SAI_BFD_SESSION_ATTR_TOS;
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attr.value.u8 = 0xC0; // CS6 for network control
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attrs.push_back(attr);
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// Create the reflector session
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sai_bfd_api->create_bfd_session(
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&sbfd_reflector_session,
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g_switch_id,
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attrs.size(),
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attrs.data());
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```
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## Usage Example: S-BFD Initiator
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The following example demonstrates how to configure an S-BFD initiator that monitors path connectivity to the reflector configured in the previous example.
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```c
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/*****************************************************
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* Create an S-BFD Initiator Session
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*
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* This initiator will:
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* - Send S-BFD packets to reflector at 192.0.2.1
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* - Use remote discriminator 4 (reflector's discriminator)
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* - Monitor path with 50ms intervals
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* - Detect failure after 3 missed packets (150ms)
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*****************************************************/
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sai_object_id_t sbfd_initiator_session;
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std::vector<sai_attribute_t> attrs;
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sai_attribute_t attr;
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// Set session type to initiator
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attr.id = SAI_BFD_SESSION_ATTR_TYPE;
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attr.value.s32 = SAI_BFD_SESSION_TYPE_INITIATOR;
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attrs.push_back(attr);
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// Set local discriminator (unique on this initiator)
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attr.id = SAI_BFD_SESSION_ATTR_LOCAL_DISCRIMINATOR;
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attr.value.u32 = 99;
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attrs.push_back(attr);
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// Set remote discriminator (reflector's well-known discriminator)
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attr.id = SAI_BFD_SESSION_ATTR_REMOTE_DISCRIMINATOR;
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attr.value.u32 = 4;
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attrs.push_back(attr);
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// Set hardware lookup valid to true
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attr.id = SAI_BFD_SESSION_ATTR_HW_LOOKUP_VALID;
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attr.value.booldata = true;
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attrs.push_back(attr);
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// Set virtual router for routing lookup
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attr.id = SAI_BFD_SESSION_ATTR_VIRTUAL_ROUTER;
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attr.value.oid = vrf_id; // Virtual router object
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attrs.push_back(attr);
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// Set source IP address (initiator's IP)
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attr.id = SAI_BFD_SESSION_ATTR_SRC_IP_ADDRESS;
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attr.value.ipaddr.addr_family = SAI_IP_ADDR_FAMILY_IPV4;
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inet_pton(AF_INET, "198.51.100.1", &attr.value.ipaddr.addr.ip4);
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attrs.push_back(attr);
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// Set destination IP address (reflector's IP)
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attr.id = SAI_BFD_SESSION_ATTR_DST_IP_ADDRESS;
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attr.value.ipaddr.addr_family = SAI_IP_ADDR_FAMILY_IPV4;
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inet_pton(AF_INET, "192.0.2.1", &attr.value.ipaddr.addr.ip4);
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attrs.push_back(attr);
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// Set UDP source port (dynamic port for this session)
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attr.id = SAI_BFD_SESSION_ATTR_UDP_SRC_PORT;
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attr.value.u32 = 49152;
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attrs.push_back(attr);
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// Set minimum transmit interval (50000 microseconds = 50 ms)
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attr.id = SAI_BFD_SESSION_ATTR_MIN_TX;
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attr.value.u32 = 50000;
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attrs.push_back(attr);
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// Set minimum receive interval (50000 microseconds = 50 ms)
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attr.id = SAI_BFD_SESSION_ATTR_MIN_RX;
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attr.value.u32 = 50000;
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attrs.push_back(attr);
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// Set detection multiplier (3 missed packets = failure)
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attr.id = SAI_BFD_SESSION_ATTR_MULTIPLIER;
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attr.value.u8 = 3;
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attrs.push_back(attr);
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// Set IP header version
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attr.id = SAI_BFD_SESSION_ATTR_IPHDR_VERSION;
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attr.value.u8 = 4;
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attrs.push_back(attr);
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// Set encapsulation type
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attr.id = SAI_BFD_SESSION_ATTR_BFD_ENCAPSULATION_TYPE;
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attr.value.s32 = SAI_BFD_ENCAPSULATION_TYPE_NONE;
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attrs.push_back(attr);
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// Optional: Set TTL
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attr.id = SAI_BFD_SESSION_ATTR_TTL;
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attr.value.u8 = 255;
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attrs.push_back(attr);
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// Optional: Set TOS/DSCP
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attr.id = SAI_BFD_SESSION_ATTR_TOS;
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attr.value.u8 = 0xC0; // CS6 for network control
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attrs.push_back(attr);
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// Optional: Enable multi-hop for non-adjacent reflector
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attr.id = SAI_BFD_SESSION_ATTR_MULTIHOP;
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attr.value.booldata = true;
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attrs.push_back(attr);
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// Create the initiator session
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sai_bfd_api->create_bfd_session(
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&sbfd_initiator_session,
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g_switch_id,
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attrs.size(),
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attrs.data());
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```
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## Usage Example: S-BFD Initiator with SRv6 Encapsulation
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The following example demonstrates how to configure an S-BFD initiator with SRv6 encapsulation for monitoring paths in an SRv6 network.
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```c
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/*****************************************************
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* Create an S-BFD Initiator Session with SRv6 Encapsulation
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*
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* This initiator will:
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* - Send S-BFD packets encapsulated in SRv6
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* - Use SRv6 segment list for path steering
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* - Monitor path with 50ms intervals
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* - Detect failure after 3 missed packets (150ms)
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*****************************************************/
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sai_object_id_t sbfd_srv6_initiator_session;
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std::vector<sai_attribute_t> attrs;
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sai_attribute_t attr;
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// Set session type to initiator
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attr.id = SAI_BFD_SESSION_ATTR_TYPE;
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attr.value.s32 = SAI_BFD_SESSION_TYPE_INITIATOR;
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attrs.push_back(attr);
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// Set local discriminator (unique on this initiator)
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attr.id = SAI_BFD_SESSION_ATTR_LOCAL_DISCRIMINATOR;
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attr.value.u32 = 99;
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attrs.push_back(attr);
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// Set remote discriminator (reflector's well-known discriminator)
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attr.id = SAI_BFD_SESSION_ATTR_REMOTE_DISCRIMINATOR;
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attr.value.u32 = 4;
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attrs.push_back(attr);
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// Set hardware lookup valid to true
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attr.id = SAI_BFD_SESSION_ATTR_HW_LOOKUP_VALID;
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attr.value.booldata = true;
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attrs.push_back(attr);
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// Set virtual router for routing lookup
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attr.id = SAI_BFD_SESSION_ATTR_VIRTUAL_ROUTER;
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attr.value.oid = vrf_id; // Virtual router object
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attrs.push_back(attr);
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// Set source IP address for inner BFD packet (initiator's IP)
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attr.id = SAI_BFD_SESSION_ATTR_SRC_IP_ADDRESS;
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attr.value.ipaddr.addr_family = SAI_IP_ADDR_FAMILY_IPV6;
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inet_pton(AF_INET6, "2001:db8:1::1", &attr.value.ipaddr.addr.ip6);
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attrs.push_back(attr);
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// Set destination IP address for inner BFD packet (reflector's IP)
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attr.id = SAI_BFD_SESSION_ATTR_DST_IP_ADDRESS;
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attr.value.ipaddr.addr_family = SAI_IP_ADDR_FAMILY_IPV6;
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inet_pton(AF_INET6, "2001:db8:2::1", &attr.value.ipaddr.addr.ip6);
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attrs.push_back(attr);
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// Set UDP source port (dynamic port for this session)
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attr.id = SAI_BFD_SESSION_ATTR_UDP_SRC_PORT;
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attr.value.u32 = 49153;
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attrs.push_back(attr);
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// Set minimum transmit interval (50000 microseconds = 50 ms)
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attr.id = SAI_BFD_SESSION_ATTR_MIN_TX;
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attr.value.u32 = 50000;
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attrs.push_back(attr);
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// Set minimum receive interval (50000 microseconds = 50 ms)
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attr.id = SAI_BFD_SESSION_ATTR_MIN_RX;
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attr.value.u32 = 50000;
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attrs.push_back(attr);
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// Set detection multiplier (3 missed packets = failure)
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attr.id = SAI_BFD_SESSION_ATTR_MULTIPLIER;
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attr.value.u8 = 3;
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attrs.push_back(attr);
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// Set IP header version for inner packet
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attr.id = SAI_BFD_SESSION_ATTR_IPHDR_VERSION;
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attr.value.u8 = 6;
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attrs.push_back(attr);
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// Set encapsulation type to SRv6
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attr.id = SAI_BFD_SESSION_ATTR_BFD_ENCAPSULATION_TYPE;
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attr.value.s32 = SAI_BFD_ENCAPSULATION_TYPE_SRV6;
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attrs.push_back(attr);
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// Set tunnel source IP (outer IPv6 header source)
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attr.id = SAI_BFD_SESSION_ATTR_TUNNEL_SRC_IP_ADDRESS;
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attr.value.ipaddr.addr_family = SAI_IP_ADDR_FAMILY_IPV6;
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inet_pton(AF_INET6, "2001:db8:100::1", &attr.value.ipaddr.addr.ip6);
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attrs.push_back(attr);
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// Set SRv6 SID list for segment routing
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// Assumes srv6_sidlist_id was created previously with desired segment list
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attr.id = SAI_BFD_SESSION_ATTR_SRV6_SIDLIST_ID;
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attr.value.oid = srv6_sidlist_id; // SRv6 SID list object
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attrs.push_back(attr);
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// Create the SRv6-encapsulated initiator session
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sai_bfd_api->create_bfd_session(
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&sbfd_srv6_initiator_session,
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g_switch_id,
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attrs.size(),
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attrs.data());

‎inc/saibfd.h‎

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@@ -50,6 +50,12 @@ typedef enum _sai_bfd_session_type_t
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/** Asynchronous Passive Mode */
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SAI_BFD_SESSION_TYPE_ASYNC_PASSIVE,
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/** S-BFD Reflector */
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SAI_BFD_SESSION_TYPE_REFLECTOR,
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/** S-BFD Initiator */
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SAI_BFD_SESSION_TYPE_INITIATOR,
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} sai_bfd_session_type_t;
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/**
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*
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* @type sai_uint32_t
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* @flags MANDATORY_ON_CREATE | CREATE_ONLY
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* @condition SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_DEMAND_ACTIVE or SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_DEMAND_PASSIVE or SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_ASYNC_ACTIVE or SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_ASYNC_PASSIVE or SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_INITIATOR
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*/
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SAI_BFD_SESSION_ATTR_REMOTE_DISCRIMINATOR,
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*
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* @type sai_uint32_t
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* @flags MANDATORY_ON_CREATE | CREATE_ONLY
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* @condition SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_DEMAND_ACTIVE or SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_DEMAND_PASSIVE or SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_ASYNC_ACTIVE or SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_ASYNC_PASSIVE or SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_INITIATOR
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*/
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SAI_BFD_SESSION_ATTR_UDP_SRC_PORT,
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*
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* @type sai_ip_address_t
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* @flags MANDATORY_ON_CREATE | CREATE_ONLY
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* @condition SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_DEMAND_ACTIVE or SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_DEMAND_PASSIVE or SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_ASYNC_ACTIVE or SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_ASYNC_PASSIVE or SAI_BFD_SESSION_ATTR_TYPE == SAI_BFD_SESSION_TYPE_INITIATOR
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*/
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SAI_BFD_SESSION_ATTR_DST_IP_ADDRESS,
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